When inspecting a bundle of similar tubes, such as those found in a heat exchanger, condenser, boiler etc., a map describing the tube layout must first be created. Normally the tubes terminate as openings in a large metal plate called a “tube-sheet”. In order to present a report on the inspected tubes, a photo or diagram of the tube-sheet must be uploaded to a computer, on which problematic tubes can then be marked. Advanced tube inspection equipment uses this map also in order to help the technician operating the equipment synchronize the tube he is inspecting at each moment with this tube's location on the tube-sheet map.
When such a photo or diagram is uploaded into the computer, the actual tube endings must be marked on it, since the software must somehow be told where the tube endings are located. Current solutions involve doing this manually, using a computer mouse for example, therefore lengthy and error prone, since tube-sheets are sometimes composed of several thousand tube openings, or tube ending.
Detecting the tube openings automatically is difficult. In the case where there is a schematic, it has often passed several rounds of photo copying; therefore the circles marking the tube ends are often faint and incomplete. In the case where this is a photo, the problem is much more difficult. Such photos are often, by necessity, taken from a short distance, facing the tube ends, using flash illumination. Therefore the tube end shapes are distorted, according to their angle from the camera, and the illumination is non-uniform. Tube endings far to the side can present themselves as darkened crescents instead of holes, whereas tube endings opposite the camera are strongly illuminated, with little shading, thus the round perimeter of the tube end might not be obvious. Such tubes and tube-sheets are often corroded and otherwise discolored, further complicating the detection. FIG. 1 illustrates an exemplary image of a common tube-sheet. As can be seen, the user had to take the image from a location that is right (from the observer side of the image) to the center of the tube-sheet and from a short distance. Consequently, the top right corner of the image is brighter than the edges; each section of the tube-sheet is differed from the others in the reflection, the shape of the opening of each tube, etc. . . .